Bought my first gun today, and am going to buy the book! In the meantime, I've been desperately searching online for info on my Smith & Wesson .22 mag revolver stamped "MOD-51" with serial "M35XXX." Is this enough info to estimate how old it is? I knew the gun was used, but wasn't thinking it was more than a year or two old - I'm delighted it may be several decades, if it is, in fact, a Model 51.